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CHAPTER 12 Management of Patient Radiation Dose During X-Ray Procedures
237
BOX 12.2 Reasons for Unacceptable
Images
• Patient mispositioning
• Incorrect centering of the radiographic beam
• Patient motion during the radiographic exposure
• Incorrect collimation of the radiographic beam
• Presence of external foreign bodies
• Postprocessing artifacts
CONCERN ABOUT RISK OF EXPOSURE DURING DIAGNOSTIC IMAGING PROCEDURES
Benefit Versus Risk
As a result of increased numbers of people in the United
States being required to and subsequently undergoing
diagnostic imaging procedures each year, concern about
the collective risk of radiation exposure from these proce-
dures continues to grow. Imaging personnel must, therefore, always strive to employ techniques that produce
high-quality images with the lowest radiation exposure.
Since the responsibility for ordering a radiologic ex-
amination lies with the referring physician, in making the
decision to order the examination, the physician must
determine whether the benefit to the patient, in terms of
medical information gained, sufficiently justifies subjecting the patient to whatever degree of risk is produced by
the absorbed radiation resulting from the procedure.
Nonessential Radiologic Examinations
Some traditional radiographic examinations are very
often casually performed in the absence of definite medi-
cal indications. This practice unnecessarily exposes the
patient to radiation even though there is virtually no
useful medical information gained from the procedure.
Examples of nonessential radiologic examinations are
described in Box 12.3.
Specifying the Amount of Radiation Received by a Patient During a Diagnostic Imaging Procedure
In general, the amount of radiation received by a patient
from diagnostic imaging procedures may be presented
in three ways:
1. Entrance skin exposure (ESE) (includes skin and
glandular)
2. Bone marrow dose
3. Gonadal dose
BOX 12.3 Unnecessary Radiologic Procedures
• A chest x-ray examination automatically scheduled on
admission to the hospital. This examination should not
be performed without clinical indications of chest disease or another important concern that justifies exposing the patient to ionizing radiation. This includes presurgical patients. A panel of physicians appointed by the
US Food and Drug Administration (FDA)
that a chest x-ray examination is not necessary for every
presurgical patient. Patients admitted for treatment of
pulmonary problems or diseases, however, may benefit
from a preadmission chest x-ray examination.
• A chest x-ray examination as part of a preemployment
physical. Very little information about previous illness or
injury can be gained through this examination, and it is
unlikely to be useful to the employer.
• Lumbar spine examinations as part of a preemployment
physical. As with the preemployment chest x-ray examination, this examination provides minimal data about previous illness or injury that would be useful to an employer.
• Chest x-ray examination or other unjustified x-ray exami-
nation as part of a routine health checkup. Radiologic
10
concluded
procedures should not be performed unless a patient
exhibits symptoms that merit radiologic investigations.
• Chest x-ray examination for mass screening for tuber-
culosis (TB). Such examinations are of negligible value
for most people. Testing for TB may be done with more
efficient procedures. However, some x-ray screening
may still be acceptable for high-risk groups such as
members of the medical and paramedical community,
people working in such fields as education and food
preparation, and selected groups of workers such as
miners and workers dealing with material such as
asbestos, beryllium, glass, and silica.
• Whole-body computed tomography (CT) screening.
Patients may elect to undergo this type of CT procedure without an order from a referring physician. They
can simply locate a facility that offers this service to the
general public. Currently, the disease detection rate
does not justify the relatively high radiation dose received by the patient from this procedure. Until there
is evidence of a significant disease detection rate,
whole-body CT screening should not be done.
3
3
238
CHAPTER 12 Management of Patient Radiation Dose During X-Ray Procedures
Although each type of specification has significance in
estimating the risk to the patient, ESE is the most frequently reported because it is the simplest to determine.
Skin Dose. Skin dose is used in radiation safety termi-
nology to refer to the dose to the epidermis, the most
superficial layers of the skin. The thickness of the epidermis varies from one anatomic area to another. It is
more substantial in areas such as the palms of the hands
and soles of the feet. The primary function of the epidermis is to protect underlying tissues and structures.
Entrance skin exposure (ESE) may be converted to
patient skin dose by using well-documented multiplication factors. These will be explicitly discussed and illustrated in several examples. When actual patient measurements are not available, reasonably accurate estimates can
still be made, which is why ESE is so widely used in assessing the amount of radiation received by a patient.
Thermoluminescent dosimeters (TLDs) are the sens-
ing devices most often used to determine skin dose directly. A small, relatively thin pack of TLDs is secured to
the patient’s skin in the middle of the clinical area of interest and exposed during a radiographic procedure. Because lithium fluoride (LiF), the sensing material in the
TLD, responds similar to human tissue when exposed to
ionizing radiation, an accurate determination of surface
dose can be made (see Table 2.5 for a list of permissible
skin entrance exposures for various radiographic examinations). In fluoroscopy, the amount of radiation that a
patient receives at the entrance surface of the skin is usually estimated by measuring the radiation exposure rate
at the tabletop* and then multiplying by the fluoroscopy
time. The placement of thermoluminescent dosimeters at
the tabletop can be used to verify that estimate.
Gonadal Dose
Difference in gonadal dose received by male and female patients. Since genetic effects may result from
exposure to ionizing radiation, protection of the reproductive organs is of particular concern in diagnostic
radiology (see Table 2.5 for a list of typical gonadal
doses from various radiographic examinations.) For
several examinations identified in Table 2.5, differences
in dose received exist between male and female patients.
*The entrance exposure rate is obtained from ionization chamber measurements with the chamber situated just beneath a
patient equivalent phantom slightly offset from the tabletop as
part of routine medical physicist equipment surveys.
Protection of the ovaries in the female patient by overlying
tissue accounts for these differences. As a consequence of
their anatomic location, the female reproductive organs
receive about three times more exposure during a given
radiographic procedure involving the pelvic region than
do the male reproductive organs. In diagnostic radiology,
the relatively low gonadal dose for a single human is by
itself considered statistically unimportant. However,
should that low gonadal dose value be applied to each
member of a large population group, then that dose value
may become far more genetically significant.
Genetically significant dose. The concept of geneti-
cally significant dose (GSD) is used to assess the overall
impact of a gonadal dose on a populace. GSD is defined
as the equivalent dose (EqD) to the reproductive organs
that, if received by every human in a large population
group, would be expected to bring about an identical
gross genetic injury to that total population, as does the
sum of the actual doses received by exposed individual
members of the population. In other words, if 5000 individual inhabitants of a population group of 500,000
each were to receive 0.05 Sv (5 rem) of gonadal radiation EqD and the other 495,000 inhabitants were not to
receive any EqD, the gross genetic effect would be identical to the effect that would occur if all 500,000 individual inhabitants each were to receive 0.0005 Sv (0.05
rem) of gonadal radiation. The concept of GSD implies,
therefore, that the genetic consequences of substantial
absorbed doses of gonadal radiation received by a small
number of individuals becomes significantly less when
averaged over an entire population rather than applied
to just a few of its members.
Additional genetically significant dose considerations.
For a population group, the GSD considers that some
people receive radiation to their reproductive organs
during a given year, whereas others do not. Also, it accounts for the fact that radiation exposure in members
of the population who cannot bear children (e.g., those
beyond reproductive years) has no genetic impact. Hence
the GSD is the average annual gonadal EqD to members
of the population who are of childbearing age. It includes
the number of children who may be expected to be conceived by members of the exposed population in a given
year. According to the US Public Health Service, the estimated GSD for the population of the United States is
approximately 0.20 millisievert (20 mrem).
Bone Marrow Dose. In humans, bone marrow is of
great importance because it contains large numbers of
CHAPTER 12 Management of Patient Radiation Dose During X-Ray Procedures
239
stem, or precursor, blood cells that could be either
depleted or, worse, even eliminated by substantial
exposure to ionizing radiation. Because irradiation of
bone marrow may be responsible for inducing leukemia,
the dose to this organ becomes very significant.3 Bone
marrow dose may also be described in terms of the
mean marrow dose, which is defined as “the average
radiation dose to the entire active bone marrow.”3 For
example, if in the course of performing a specific radiographic procedure, 25% of the active bone marrow were
in the useful beam and received an average absorbed
dose of 0.8 mGyt, the mean marrow dose would be
0.2 mGyt, Because multiple bony areas span the entire
body, the radiation dose absorbed by the organ that is
called “bone marrow” cannot be measured accurately by a
direct method; it can only be estimated. In diagnostic radiology, the bone marrow dose is one of the values that has
been used to provide an approximation of patientabsorbed doses even though hematologic effects are generally negligible for doses associated with this modality.
Table 2.5 provides typical bone marrow doses for
various radiographic examinations performed on human
adults. The levels indicated in Table 2.5 are usually less for
children because the active bone marrow is more evenly
spread out, and significantly lower technical radiographic
exposure factors are used. Although each dose listed in
Table 2.5 results from fragmentary exposure of the human body, it is averaged over the whole body.
Fluoroscopically Guided Positioning
Fluoroscopic guided positioning (FGP) is the practice
of using fluoroscopy to determine the exact location of
the central ray before taking a radiographic exposure.11
Some radiologic technologists (RTs) believe that the
use of FGP results in less dose to the patient than does
a repeat radiograph. However, the ASRT adopted the
following positioning statement:
The ASRT recognizes that the routine use of fluoroscopy to ensure proper positioning before making an
exposure is an unethical practice that increases patient
dose unnecessarily and should never be used in place of
appropriate skills required of a competent radiologic
technologist.
Even though the ASRT does not condone FGP, some
imaging facilities continue to allow RTs to use fluoroscopy as a positioning aid because they believe that it:
• Is faster than having a repeat exposure
• Reduces the number of repeat exposures
• Provides less radiation exposure to the patient
12
The Standard of Ethics as published by the American Registry of Radiologic Technologists (ARRT)
serves as a guide for practicing technologists in maintaining a high level of ethical conduct and in providing for the protection, safety, and comfort of patients.13 Blind positioning, or positioning using the
radiographer’s skill and the anatomic landmarks on
the patient, without a repeat exposure, provides the
patient with the lowest dose. However, some technologists argue that the chance of repeating the image is
reduced when using FGP. This argument does not hold
true according to the current repeat rates of 7% to
8%.14 For example, if a technologist has a repeat rate
of 10%, it would not be ethical to overexpose 90% of
the patients with FGP to lower the repeat rate. Thus,
the usage of FGP by technologists is a practice that
should be avoided. It is prohibited by many state regulatory agencies. Where FGP is permitted, the repeat
rate depends on the:
• Technologists’ skills in the operation of the fluoro-
scopic equipment
• Communication between the technologist and the
patient
• Patients’ cooperation
• Patients’ condition
Therefore, the chance of a repeat during an FGP examination is still present, and ultimately it is the technologist’s professional responsibility to reduce the amount of
radiation exposure to all patients, not just those who may
need to have a repeat examination.
Studies indicate that patient ESE increases with the
use of FGP when a repeat exposure is needed.15 Blind
positioning provides the lowest patient ESE.
The current scientific consensus is that all dose
levels of ionizing radiation have a non-zero potential
for producing detrimental effects (the linear nonthreshold concept previously discussed). At the same
time, however, procedures in radiology, such as fluoroscopy and other imaging modalities, are providing
vital information to physicians for diagnosis or treatment of disease. Thus, risk versus benefit must always
be considered.
Exposure of patients to medical x-rays is commanding increasing attention in society for two
reasons:
1. The frequency of x-ray examinations, including
many repetitive studies in short periods, among all
age groups, is expanding annually. This increase in-
dicates that physicians are relying more and more on
240
CHAPTER 12 Management of Patient Radiation Dose During X-Ray Procedures
radiologic examinations to assist them in patient
care and diagnosis.
2. Concern among public health officials is growing
regarding the risk of late effects associated with these
multiple medical x-ray exposures.
A review of the literature emphasized the following
guidelines:
• No diagnostic procedure using ionizing radiation
should be conducted unless its benefit outweighs
its risk.
• Exposures should be kept ALARA, with the procedure optimized to reduce radiation hazards.
• The ESE dose level specified in regulations must not
be exceeded.
• To maintain ALARA and follow the ASRT position
statement and the ARRT code of ethics, technologists
must not use FGP positioning of patients.
3
PROTECTING THE PREGNANT OR POTENTIALLY PREGNANT PATIENT
Position of the American College of Radiology on Abdominal Radiologic Examinations of Female Patients
Because much evidence suggests that the developing
embryo-fetus is very radiation-sensitive, special care is
taken in radiography to prevent unnecessary exposure
of the abdominal area of pregnant women. Unfortunately, many women are not aware that they are pregnant during the earliest stage of pregnancy, and this
means that exposure to the abdominal area of potentially pregnant (i.e., fertile) women are a concern.
When the referring physician does not consider radiologic procedures urgent, they may be regarded as elective examinations. They can be booked at an appropriate time to meet patients’ needs and safety requirements.
However, the official position of the ACR, the primary
professional organization of radiologists in the United
States, is as follows:
“Abdominal radiological examinations that have been
requested after full consideration of the clinical status
of a patient, including the possibility of pregnancy,
need not be postponed or selectively scheduled.”
Although elective scheduling is not always at-
tempted in departments with high workloads, it is the
16,17
15
policy of some facilities that women of childbearing
years should be made aware of the NCRP recommendations and given a choice as to when they want to
have a non-urgent abdominal examination. The NCRP
recommendation states that abdominal examinations
should be performed during the first few days after
the onset of menses to minimize the possibility of
irradiating an embryo.
17,18
Determining the Possibility of Pregnancy
Whenever a female patient of childbearing age is to
have an x-ray examination, it is essential that beforehand the radiographer carefully question the patient
regarding any possibility of pregnancy. Part of this questioning involves asking the patient for the date of her
last menstrual period (LMP). If the patient is to receive
substantial pelvic irradiation and there is doubt about
her pregnancy status, then, provided there are no overriding medical concerns, it is strongly recommended
that the result of a pregnancy test be obtained before the
pelvis is irradiated.
Irradiation During an Unknown Pregnancy
Even with precautionary steps, it is likely that a radiographer will encounter many occasions when a
patient who was confident that she could not be pregnant later discovered that she was pregnant at the time
of her x-ray examination. This revelation is usually
communicated to the imaging department by the patient’s obstetrician and is accompanied by a request
for the amount of radiation dose that the patient’s
embryo-fetus received from the x-ray study. The following discussion attempts to illustrate in a simplified
manner how the radiography team can appropriately
respond to such queries by presenting several case
examples.
The first step in the process is to list the specifics of
the x-ray examination in as much detail as possible. A
useful form can be developed to assist in this process
(Fig. 12.7). The information that is needed to fill out
this form is listed in Box 12.4.
The following question sometimes arises if a pregnant patient is inadvertently irradiated. Should a therapeutic abortion be performed to prevent the birth of
an infant because of radiation exposure during pregnancy? Studies of groups such as the atomic bomb
survivors of Hiroshima have shown that damage to
CHAPTER 12 Management of Patient Radiation Dose During X-Ray Procedures
Facility: _______________________________________________________________________
Imaging Department
REQUEST FOR PATIENT RADIATION DOSE
PATIENT X-RAY EXAM RECORD
241
Patient’s name: _____________________________________
Date of birth: _______________________________________
Date of last menstrual period: ___________________________________________________
Referring physician: ___________________________________________________________
Physician requesting radiation dose: _____________________________________________
Radiologist: __________________________________________ Radiographer: ______________
Examination: _________________________________________ X-ray room unit: ____________
RADIOGRAPHIC
Projection
Anatomic
location
Anatomic
location kVp mA
Patient
thickness Film kVp mAs SID
FLUOROSCOPIC
kVp
(mean)
mA
(mean)
SPOT FILMS
Time
(msec)
X-ray study #: _____________
Exam date: _______________
Number
of images
Fluoro
time
Number
of spots
Gonadal
shield
Exam
description
Special
details
Fig. 12.7 Request for patient radiation dose form.
the newborn is unlikely for doses below 0.2 Gy. Because essentially, all diagnostic medical procedures
result in fetal exposures of less than 0.01 Gy (1 cGy),
the risk of abnormality is minimal. The position of
the NCRP is stated in Box 12.5.
17
Procedure to Follow and Responsibility for Absorbed Dose Determination to the Patient’s Embryo-Fetus
When the details of the x-ray examination have been
collected and listed on an appropriate summary form,
242
CHAPTER 12 Management of Patient Radiation Dose During X-Ray Procedures
BOX 12.4 Information Needed to
Develop the Request for Patient Radiation
Dose Form
• The x-ray unit or units used for the study
• The projections taken
• The number of images associated with each exami-
nation
• Each projection’s technical exposure factors (kVp,
mAs, image receptor size)
• The source-to-image receptor distance (SID) for each
projection
• The patient’s anteroposterior (AP) or lateral dimensions
at the site of each projection
• For fluoroscopic irradiation, the approximate kVp,
mA, and especially the duration
• For spot images, the number taken, the kVp and mA
selected, and the approximate exposure time
BOX 12.5 Position of the National
Council on Radiation Protection and
Measurements Concerning Risk and Fetal
Exposure Regarding the Termination
of Pregnancy
This risk is considered to be negligible at a fetal absorbed dose of 5 cGy or less when compared with other
risks during pregnancy. The chance of malformations is
significantly increased above control levels only at doses
beyond 15 cGy. Therefore, the exposure of the fetus to
radiation arising from diagnostic procedures would
rarely by cause, by itself, for terminating a pregnancy.
If there are reasons other than possible radiation effects to consider a therapeutic abortion, the attending
physician should discuss those reasons with the patient
so that it is clear that the radiation exposure is not being
used as an excuse for terminating the pregnancy.
Adapted from National Council on Radiation Protection and
Measurements (NCRP): Radiation protection in pediatric
radiology, Report No. 68, Washington, DC, 1977, NCRP.
data list supplied by the radiographer. It also uses published absorbed dose data tables. What eventually is
obtained and presented by the medical physicist, radiologist, or radiation safety officer to the patient’s physician is a calculated estimate of the approximate EqD to
the embryo-fetus due to the x-ray examination.
Sample Cases to Estimate Approximate Equivalent Dose to the Embryo-Fetus
Several typical cases (somewhat simplified) are presented to illustrate one of the methods that may be used
to obtain this calculated estimate. Here, it is not the
purpose to provide an advanced presentation, but instead, to offer a basic method that makes use of fundamental principles and demonstrates the importance of
the radiographer’s input in the process. The most significant factor is the correction to the measured radiation output at a given kVp due to the patient’s anatomical thickness and the distance from the image
receptor to the tabletop. The product of the radiation
output dose rate at the patient’s radiation entrance surface (mGya/mAs) at the kVp selected and the mAs used
for the x-ray projection considered yields the ESEd for
that projection, a quantity that needs to be obtained for
each x-ray exposure given to the patient. The most
common measurements of milligray per mAs are at a
distance of 100 cm from the x-ray tube target. These
values as a function of kVp and mAs are usually tabulated during each annual survey of the x-ray unit by a
qualified medical physicist. For a patient with thickness
T in centimeters and a typical distance of 8 cm from the
image receptor to the tabletop, the radiation output at
the patient’s entrance surface for selected mAs is determined as shown in Fig. 12.8, which illustrates all the
geometric quantities of interest.
Since the skin surface is closer to the x-ray tube target, the milligray per mAs value will be greater than it is
at 100 cm. How much greater is determined from the
inverse square law and given by Equation 12.1 below:
they must be conveyed to the radiation safety officer or
to the medical physicist providing x-ray quality assurance services. It is then that individual’s task to determine the absorbed EqD to the patient’s embryo-fetus.
The calculation process makes use of actual measurements of radiation output on the individual x-ray unit
or units and incorporating that with the examination
(mGy /mAs) at kin surface
a
(mGy /mAs) at
1100 cm (100/[92 25])
s
a
As an example, assume the following values:
(mGy /mAs) at 100 cm 0.06
a
T 25 cm
5
5
2
CHAPTER 12 Management of Patient Radiation Dose During X-Ray Procedures
ESE
Tube target
X
(40 inches)
Entrance surface
Tabletop
8 cm
(3 inches)
Fig. 12.8 As the diagram shows, the distance from the tube target to the tabletop is 100 cm (40 inches)
minus 8 cm (3 inches). The distance from the tube target to the top of the patient in centimeters is therefore
equal to 100282T where the patient’s thickness, T, is specified in centimeters. To convert this value to inches
just divide by 2.54.
Patient
Image receptor
T (cm)
243
100 cm
SID
Then:
(mGy /mAs) at skin surface 0.06 (100/67
a
))
0.06 (100/2.23)
0.13 mGy /mAs
2
a
The patient’s ESEd for an x-ray exposure is now given
by Equation 12.2 and obtained as shown:
(mGy /mAs) at skin surface mAs use
dd
d a
Example:
mAs used 30
(mGy /mAs) 0.13
a s
ESE 0.13
d
30
3.9 mGy
After the ESEd has been determined for each x-ray
exposure, it is necessary to obtain conversion factors
that will yield a value for the uterine absorbed dose
attributable to each exposure. In 1977, the NCRP
published Report No. 54, Medical Radiation Exposure
of Pregnant and Potentially Pregnant Women. Table 4 in
this report has been a valuable resource for helping
establish the uterine dose. Although other useful and
more recent data tables exist, this table has been reproduced here as Table 12.1 to illustrate a simple method
for fetal dose estimation. To use the table, it is necessary
to know for each x-ray projection the ESEd, the anatomic
location, the beam quality (half-value layer [HVL]), and
the image receptor size.
Sample Cases to Obtain an Approximate Estimate of the Fetal Equivalent Dose
Two typical x-ray examinations will be considered, and
an approximate estimate of the fetal EqD resulting from
each study obtained. These are presented in detail in
boxes labeled as Case 12.1 and Case 12.2.
Irradiating a Known Pregnant Patient
If the physician believes it is in the best interest of a
pregnant or potentially pregnant patient to undergo a
radiologic examination, the examination should be
performed and extra efforts made to minimize the
dose of radiation the patient receives to her lower
abdomen and pelvic regions. This can be accomplished by consciously selecting the smallest technical
exposure factors that will still yield a diagnostically
acceptable image for the examination and by precisely
collimating the radiographic beam to include only
the anatomic area of interest. When the patient’s
lower abdomen and pelvic regions do not have to be
244
CHAPTER 12 Management of Patient Radiation Dose During X-Ray Procedures
TABLE 12.1 Embryo (Uterine) Doses for Selected X-Ray Projections (mcGy/R)*
BEAM QUALITY (HVL MM ALUMINUM)
Anatomy
or Study Projection
Pelvis,
lumbopelvic
Abdominal
Lumbar spine AP 40 14 3 17 128 189 250 309 366 419
Hip AP (1) 40 10 3 12 105 153 200 244 285 324
Full spine
(chiropractic)
Urethrogram AP 40 10 3 12 135 200 265 327 386 441
Upper GI AP 40 14 3 17 9.5 16 25 34 45 56
Femur (one side) AP 40 7 3 17 1.6 3.0 4.8 6.9 9.4 12
Cholecystography PA 40 10 3 12 0.7 1.5 2.6 4.1 6.0 8.3
Chest AP 72 14 3 17 0.3 0.7 1.3 2.0 3.1 4.3
Ribs, barium
swallow
Thoracic spine AP 40 14 3 17 0.2 0.4 0.8 1.4 4.1 3.0
Skull, cervical
spine, scapula,
shoulder,
humerus
AP, Anteroposterior; GI, gastrointestinal; HVL, half-value layer; LAT, lateral; PA, posteroanterior; SID, source-to–image receptor
distance.
*Average dose to the uterus in millicentigray per roentgen entrance skin exposure (free-in-air) (ESE
is essentially equal, in these energy ranges, to 10 mGy ESEd or 1 cGy ESEd.
†
Adapted from NCRP report No. 54 Rosenstein (1976).
‡
Field size is collimated to the image receptor.
§
Includes retrograde pyelogram; kidney, ureter, and bladder (KUB); barium enema, lumbosacral spine, intravenous pyelogram (IVP);
renal arteriogram.
Data modified from National Council on Radiation Protection and Measurements (NCRP): Medical exposure of pregnant and
potentially pregnant women, Report No. 54, Washington, DC, 1977, NCRP.
§
AP 40 17 3 14 142 212 283 353 421 486
LAT 40 14 3 17 13 25 39 56 75 97
AP 40 14 3 17 133 199 265 330 392 451
PA 40 14 3 17 56 90 130 174 222 273
LAT 40 14 3 17 13 23 37 53 71 91
LAT 40 14 3 17 9 17 27 39 53 69
AP (2) 40 17 3 14 136 203 269 333 395 454
AP 40 14 3 36 154 231 308 384
PA 72 14 3 17 0.3 0.6 1.2 2.0 3.0 4.5
LAT 72 14 3 17 0.1 0.3 0.5 0.8 1.2 1.8
AP 40 14 3 17 0.1 0.3 0.5 0.9 1.4 2.0
PA 40 14 3 17 0.1 0.3 0.5 0.9 1.5 2.2
LAT 40 14 3 17 0.03 0.08 0.2 0.3 0.4 0.6
LAT 40 14
— 40 — ,0.01 ,0.01 ,0.01 ,0.01 ,0.01 ,0.01
SID
(Inches)
Image Receptor
Size (Inches)
3 17 0.04 0.1 0.2 0.4 0.5 0.8
‡
1.5 2.0 2.5 3.0 3.5 4.0
). The latter value in roentgens
d
†
457 527
included in the area to be irradiated, they should be
protected with a lead apron or other suitable protective shield so that a developing embryo- fetus does not
receive unnecessary radiation exposure from external
scatter and the edges of the selected radiation field
(Fig. 12.9).
PEDIATRIC CONSIDERATIONS DURING RADIOGRAPHIC IMAGING
Vulnerability of Children to Radiation Exposure
Children are much more vulnerable to the late effects
of radiation than are adults. Hence, children require
CHAPTER 12 Management of Patient Radiation Dose During X-Ray Procedures
CASE 12.1 Obstruction Series
X-ray projection details:
Although a 180 cm (72 inch) source-to-image receptor
distance (SID) would normally be used for a posteroanterior (PA) upright chest projection, for purposes if simplifying the calculation, the SID will be kept at 100 cm (40 inch)
the same for all projections in this series.
PA chest projection
(1) 80 kVp, 10 mAs, 100 cm SID, large CR image recep-
tor, 25-cm patient thickness Erect anteroposterior
(AP) abdomen
(1) 75 kVp, 32 mAs, 100 cm SID, large CR image recep-
tor, 20-cm patient thickness Supine abdomen
(1) 70 kVp, 50 mAs, 100 cm SID, large CR image recep-
tor, 20-cm patient thickness
Calculation:
The first step is to obtain the value of mGy
projection. To determine this value, a reference value
(mGy
/mas)
a
the kVp used. To comply with state rules and regulations,
a medical physicist measures these values yearly for each
x-ray tube. If the measured reference mGy
for the three projections are 0.01, 0.04, and 004, respectively, then substituting these numbers into Equation 12.1
along with the corresponding SIDs and patient thicknesses yields: (mGy
erect AP abdomen 5 0.08, and supine abdomen 5 0.08,
respectively. From Equation 12.2 the entrance skin exposure does (ESE
ESE PA chest: 0.02 10 0.2 mGy 0.02 cGy
d
ES
EE erect AP abdomen: 0.08 32 2.5 mGy 0.26
d
ESE s upine a bdomen: 0.08 50 4 mGy 0.4
d
is needed for the x-ray unit involved and
100-cm
/mAs)s PA chest 5 0.02 (mGya/mAs)
a
) value is then given by:
d
ccGy
cc Gy
/mAs for each
a
/mAs values
a
For the chest field, the half-value layer (HVL) is approximately 3 mm aluminum (Al), whereas for the abdominal
fields, 2.5 and 2.0 mm Al, respectively, are used. Then
from Table 12.1 the embryo/uterine dose conversion factors are 2 mcGy/(cGy of ESE
and 199 mcGy/(cGy of ESE
the ESE
(FDE) for each, namely:
PA chest FDE 0.02 2 0.04 mcGy (.04 mi lllirads)
Erect AP abdomen FDE 0.26 265
Supine a bdomen FDE 0.4 199
1 millirad)
mcGy 5 1.49 mGy. For diagnostic x-rays, 1 mGy is the
same as an equivalent dose of 1 mSv, and consequently
the calculated approximate EqD to the patient’s embryofetus from her obstruction series is 1.49 mSv (149 millirem).
s,
embryo-fetus is substantially less than the 5 mSv (500
mrem) recommended by the National Council on Radiation Protection and Measurements as a maximum EqD to
the embryo-fetus during the 9 month gestation period.
for each projection gives a fetal dose estimate
d
(Note: 1 cGy 5 1 rad and therefore 1 millicGy equals
The total FDE is therefore 0.04 1 69 1 79.6 5 149
For reference purposes this value of EqD to the
), 265 mcGy/(cGy of ESEd),
d
). Multiplying these values by
d
69 mcGy (69 millirads)
79.6 mcGy (79.6 millirads)
245
special consideration when they undergo diagnostic
x-ray studies. Some of these considerations are described in the following sections. Because children have
a greater life expectancy, they may easily survive long
enough to develop late effects like leukemia or another
radiogenic malignancy such as lung or thyroid cancer.
According to studies published in 1978, the risk of radiation-induced leukemia in children after a substantial
dose of ionizing radiation is approximately two times
that of adults.19 For low doses such as those generally
encountered in conventional diagnostic radiology,
data are still inconclusive. With this concern in mind,
radiographers must take every precaution to minimize
exposure in all pediatric patients.
Children Require Smaller Radiation Doses Than Do Adults
In general, smaller doses of ionizing radiation are sufficient to obtain useful images in pediatric imaging
procedures than are necessary for adult imaging procedures. For example, an entrance exposure dose below
5 millicGy (mcGy, previously millirads: mrads) results
from an AP projection of an infant’s chest,20 whereas
the same projection or a PA projection of an adult’s
246
CHAPTER 12 Management of Patient Radiation Dose During X-Ray Procedures
CASE 12.2 Modified Upper Gastrointestinal Examination
X-ray projection details:
Fluoroscopy: 115 kVp, 4.5 mA (mean values), 3.5 minutes
Spot images (4): 110 kVp, 200 mA, 20 msec (mean values)
Calculation:
Suppose that from measured data on the involved fluoroscopic unit, the entrance exposure rate dose to the patient is about 12.5 mGy per milliampere minute. Therefore,
the entrance skin exposure dose (ESE
fluoroscopic radiation is obtained from the product:
12.5 mGy/mAmin 4.5 mA 3.5 min 197 mGy (19.7 cGy)
From measured spot image radiation output, for the
technique factors used in this study, let the x-ray output at
the patient’s entrance surface be 0.5 mGy/mAs.* Therefore, the total ESE
4 0.5 mGy/mAs 200 mA 0.020 sec 8 mG yy (0.8 cGy)
Using half-value layer (HVL) values 4.0 and 3.5 mm aluminum (Al), respectively, the uterine dose rates obtained
from Table 12.1 are as follows:
Averaged fluoroscopic irradiation: 56 mcGy/cGy 5 56 mrem/
cGy (entrance dose factor)
for the four spot images is given by:
d
) for the delivered
d
Spot image: 45 mcGy/cGy 5 45 mrem/cGy (entrance
dose factor)
The estimated approximate equivalent dose to the
embryo-fetus from this modified upper gastrointestinal
(UGI) study is then:
56 19.7 45 0.8 1139 mrem 1.14 rem 11.4 mSv
For this modified UGI study on a heavy patient, a fetal
EqD estimate has been obtained that is more than twice
the National Council on Radiation Protection and Measurements recommended maximum fetal EqD of 5 mSv
(0.5 rem). This result, however, is far below the range
between 100 and 200 mSv (10 and 20 rem) at which
therapeutic abortion has historically been considered. If
the embryo-fetus were in its most sensitive stage (i.e.,
early first trimester), then possibly some genetic studies
could be undertaken. Other wise, in most situations, increased follow-up would be the course of action.
*For the spot images the entrance surface of the patient is only about 46 cm (18 inch) from the x-ray tube target, and that is why
the value of mGy/mAs can be so high.
children to understand the radiologic procedure and,
in most cases, their imperfect ability to cooperate,
these children are less likely to remain still during a
radiographic or fluoroscopic exposure. To solve or at
least minimize this problem, the radiographer must
employ very short exposure times by selecting a highmA (400 mA or greater) station and using effective
immobilization techniques. For some examinations,
such as chest radiography, individual pediatric motion
restriction devices are available to hold the pediatric
Fig. 12.9 To protect a developing embryo-fetus from unneces-
sary radiation exposure, place a lead apron over the female
patient’s lower abdomen and pelvic regions when these sites
do not have to be included in the area to be irradiated.
patient securely and safely in the required position (see
Fig. 12.4). Such procedures and correct image postpro-
cessing techniques dramatically reduce or eliminate
the need for repeat examinations that will increase
patient dose.
chest yields entrance exposure doses that can range
from 10 to 25 mcGy.
Gaining Cooperation During the Procedure
Combining technologists who have experience work-
Patient Motion and Motion Reduction Methods
Patient motion is frequently a problem in pediatric radiography. Due to the limited ability of very young
ing with children with examination rooms specially
designed for pediatric studies is very beneficial. These
rooms contain not only appropriate restraint devices,